The regulation of cAMP and CA++ accumulation by vascular smooth muscle cells (SMC) grown in culture from aortas of normotensive Wistar-Kyoto (WKY) and spontaneously hypertensive rats (SHR) was explored. No differences in the rate or extent of cAMP or Ca++ accumulation were observed when SMC from WKY, SHR or stroke-prone SHR were compared. Beta-agonists, and to a lesser extent vasoactive intestinal polypeptide, forskolin, PGE1 and PGE2, increased cAMP levels. Of all treatments studied, only angiotensin II and high extracellular K+ were capable of enhancing Ca++ uptake. Exposure of SMC and vascular fibroblasts (used as control vascular cells) to dibutyryl cAMP led to morphological changes in both cell types characterized by cytoplasmic shrinking and cellular elongation. However, only SMC exhibited morphological changes following exposure to Beta-agonists, which were potent stimulators of cAMP production in SMC, but not in fibroblasts. colchicine reversed the morphological changes associated with cAMP accumulation, suggesting the participation of cellular microtubules in cytoplasmic shrinking. These studies have allowed us to develop a useful model system to study the cellular biology of SMC and the biochemical differences between SMC derived from WKY and SHR in a milieu isolated from the complexities of the intact organism.